Method of recycling construction and demolition debris

ABSTRACT

A method of recycling construction and demolition debris produces a product useful in earth engineering applications, including landfills, soil stabilization and roadbeds. The method involves wet shredding construction and demolition debris into a moist shredded product and applying the product as daily cover for a landfill, or in a roadbed, or as a soil stabilizer or nutrient. A landfill design using the recycled product is also disclosed.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a continuation-in-part of U.S. Pat. application Ser. No.07/883,354 filed May 15, 1992, which is a continuation-in-part of U.S.Pat. application Ser. No. 07/871,103 filed Apr. 20, 1992, now U.S. Pat.No. 5,181,803.

FIELD OF THE INVENTION

The present invention relates to a method of recycling construction anddemolition debris. More particularly, the invention relates to a methodof recycling construction and demolition debris into an article usefulin earth engineering applications, such as municipal solid wastelandfills, roadbeds, soil stabilization, soil erosion control and thelike.

BACKGROUND OF THE INVENTION

Federal and state environmental regulations require the operators ofsanitary landfill operations to periodically cover disposed solid wastewith six inches of earthen material to control disease, insects, fires,odors, blowing litter, and scavenging. For example, most jurisdictionsrequire such covering of sanitary landfills at the end of each operatingday, or at more frequent intervals if necessary. This coveringrequirement and the cover material is known as "daily cover" or"periodic cover" where the regulatory interval is more than one day,e.g., three days. As used herein, "daily cover" is intended to includedaily and periodic cover for sanitary landfills, such as municipal solidwaste (MSW) landfills, rubble landfills, land clearing debris landfills,and industrial waste landfills.

Each day's garbage, trash or rubble layer is covered at the end of theday and further garbage, trash or rubble layers are then spread directlyon top of the daily cover from the previous day. In many landfill sitesthe soil used for the daily cover must be mined at the landfill site orpurchased from an outside source and, due to the high rate of soilconsumption, comprises a substantial cost item. Moreover, it has beenrecognized that multiple earth fill layers used in this way consume asignificant volume of the valuable landfill space which might otherwisebe used for receiving garbage, trash or rubble. It is well known thatmany communities are rapidly exhausting their available landfill acreageand it is therefore desirable to reduce the consumption rate of theavailable landfill volume. Accordingly, federal and state regulationsallow alternative, more compressible, daily cover materials in lieu ofthe six inches of earthen material so long as the alternative materialsprovide the requisite level of protection.

One known solution to reducing the volume of municipal solid wastelandfills is to shred the municipal solid waste to achieve a greaterfilling density in the landfill. One example of this solution isdisclosed in U.S. Pat. No. 4,834,300 to Wojciechowski et al. whichdescribes a process of reducing municipal solid waste to dry particlesof a relatively small, uniform size to be mixed with the earth of alandfill for minimizing settlement and maximizing the load supportcapabilities of the landfill. While this process for forming a municipalsolid waste landfill may be acceptable in some jurisdictions, it doesnot provide the daily cover required by the great majority ofjurisdictions.

Some jurisdictions permit disposal of municipal solid waste in alandfill in shredded form without a requirement for daily cover.Although this method for disposal is accepted in some instances, itstill has serious health and environmental drawbacks compared tolandfills which require daily cover.

The prior art also does not adequately address the problem of disposingof construction and demolition debris in an efficient, useful and/orspace saving manner. Rubble landfills in which construction anddemolition debris is typically disposed consume a substantial volume ofavailable landfill space. It would be desirable therefore to provide amethod of recycling construction and demolition debris in a way whicheliminates the need for rubble landfills and in which substantially theentire volume of construction and demolition debris can be recycled andmade use of in other earth engineering applications.

SUMMARY AND OBJECTS OF THE INVENTION

In view of the foregoing limitations and shortcomings of the prior art,as well as other disadvantages not specifically mentioned above, itshould be apparent that there still exists a need in the art for an amethod of recycling construction and demolition debris in an efficient,cost effective, and space saving manner, and especially a method inwhich recycled construction and demolition debris can be effectivelyutilized in various earth engineering applications.

More particularly, it is an object of this invention to provide a newmunicipal solid waste landfill construction having a greater density andcompressibility than prior art constructions.

It is another object of this invention to provide a product useful inearth engineering applications which includes recycled construction anddemolition debris.

Yet another object of this invention is to provide a method of disposingof construction and demolition debris in a manner that isenvironmentally sound and practical.

The aforementioned objects are accomplished according to the inventionby a method of converting or recycling construction and demolitiondebris into an article for use in earth engineering applications."Construction and demolition debris," as used herein and as typicallydefined by state and municipal laws and ordinances, comprises debrisassociated with the razing of buildings, roads, bridges, and otherstructures and/or debris associated with the construction of buildings.It typically includes, but is not limited to, ferrous and non-ferrousmetals, concrete, bricks, lumber, plaster and plasterboard, insulationmaterial, cement, shingles and roofing material, floor, wall and ceilingtile, asphalt, glass, pipes and wires, carpet, wallpaper, felt and otheritems physically attached to the structure, including compactedappliances, structural fabrics, paper or cardboard packaging. Theforegoing definition of construction and demolition debris is notintended to exclude debris, all or substantially all of which comprisespaper, paperboard, paper cartons, cardboard and the like, such as isincluded, for example, in what is referred to in the art as "commercialwaste." Commercial waste typically includes waste from office buildings,business establishments and other commercial enterprises which producelarge quantities of paper, paper-based office-type waste and other wasteproducts associated with such commercial enterprises, e.g., woodencrates and packing, metal, strapping, plastic, furniture, officeequipment and glass. Thus, commercial waste is intended to be includedin construction and demolition debris as that term is used herein.Typically excluded from construction and demolition debris are materialsthat pose an undue risk to public health or the environment such asindustrial waste or byproducts, paint, tar, solvents, creosote,adhesives and the like.

It is not intended that the above listing of specific debris items beall-inclusive of the items of debris which may be incidentally presentin construction and demolition debris. It is within the contemplationand scope of the present invention that limited or incidental amounts ofother debris items may be present in construction and demolition debriswithout altering either its essential characteristics as constructionand demolition debris or its suitability for recycling according to themethod of the invention. Such other debris items may include, e.g.,tires, brush and limbs, rock, etc.

In some cases, construction and demolition debris must be deposited inwhat are commonly known as "rubble" landfills which are required tosatisfy stringent design and operational requirements. However,according to the method of the present invention, the construction anddemolition debris is converted into a useful product which can be usedin many applications, such as a daily cover for a sanitary landfillrather than being disposed of as the contents of the landfill. Thisdaily cover can be used not only for municipal solid waste, landclearing debris and rubble landfills, but also for industrial wastelandfills which are subject to even stricter regulation.

Briefly described, the method of the invention comprises the steps ofremoving large pieces of metal from the debris, compacting the balanceof the debris into small pieces, wet shredding the pieces into evensmaller particles, separating the ferrous and optionally the non-ferrousmetals from the debris utilizing the combination of magnetic, air and/orwater separating systems, and dewatering the wet shredded debris toproduce a product suitable for the aforementioned applications.

The product of the present invention when used in a landfill alsoadvantageously functions as a more effective filter medium than theconventional earthen daily cover materials thereby resulting in acleaner leachate arriving at the bottom of a landfill using the productof the invention as daily cover. The product of the method of theinvention may thus be used in a landfill as daily cover and as a filtermedium. Alternatively, the product may be used as a filter medium tofilter a liquid stream in applications other than landfills as well as afilter medium for liquid streams in landfill operations.

A further advantage of the present invention resides in the fact thatconstruction and demolition debris includes items, such as cement,concrete, plaster board and the like, containing calcium oxide or lime.The presence of these ingredients in a daily cover layer thusadvantageously reduces the acidity level of the leachate reaching thebottom of the landfill site.

The product of the invention comprising the converted or recycledconstruction and demolition debris may also be used as daily cover in anovel municipal solid waste landfill or sanitary landfill constructionmade according to the present invention. Other uses according to theinvention of the converted or recycled construction and demolitiondebris include roadbeds, especially temporary roadbeds, soilstabilization and/or soil erosion control, a soil nutrient or topsoil,especially when mixed with fly ash or sludge, and other earthengineering applications.

With the foregoing and other objects, advantages and features of theinvention that will become hereinafter apparent, the nature of theinvention may be more clearly understood by reference to the followingdetailed description of the invention, the appended claims and to theattached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flow diagram in block form showing the present invention inthe stages which can be used in the course of recycling the constructionand demolition debris into a product;

FIG. 2 is a fragmentary cross-section of a municipal solid wastelandfill structure using the product made according to the method of theinvention; and

FIG. 3 is a fragmentary cross-section of a temporary roadbed using theproduct made according to the method of the invention.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to FIG. 1 wherein there is illustrated a flow diagram inblock form showing the preferred stages utilized in the course ofrecycling construction and demolition debris according to the presentinvention.

The process begins with the transport of construction and demolitiondebris to a processing center as shown in block 10 of the drawing. Afterthe construction and demolition debris arrives at the processing center,large pieces of metal are removed from the debris by a crane and placedin a collection area as shown in blocks 12 and 14 of FIG. 1.

The balance of the material is then moved to a "compacting" area whereit is compacted as seen in block 16 of FIG. 1. Compacting is the processof reducing the size of the material ("presizing") to allow it to bemore efficiently fed to and processed by a shredder. A wheel compactormachine is typically used for compacting. One suitable machine that hasbeen found effective in this compacting or presizing process is theIngersoll Rand 750 Wheel Landfill Compactor. This compactor has spikedwheels which grind and cut the debris into smaller pieces in the processof compacting it. Other types of compacting machines may also be used.

After compacting, the material is fed into a shredding apparatus asshown in block 18 where it is reduced to even smaller pieces having anaverage particle size of six inches or less and preferably an averageparticle size of three inches or less. As used herein, "average particlesize" means the average sizes of all particles where the particle sizeis determined by the average of the particle dimensions. Thus, anindividual particle may have a dimension well in excess of six inches solong as the average dimensions of that particle and all other particlesaverage less than six inches, or preferably three inches.

The compacted debris is loaded onto a steel belt conveyor whichtransports the material into the inlet of the shredder. One shredderwhich has been found to be especially suitable for purposes of theinvention is an automotive shredder known as the Newell Super Heavy DutyShredder Model No. 80104TBD manufactured by Newell Industries, Inc. ofSan Antonio, Tex. The Newell shredder has a rotor diameter of 80" and awidth of 104" and is powered by a 3000 hp electric motor. The Newellmachine is configured as a "wet shredder" because water is addeddirectly into the shredding chamber which houses the rotor in order toprevent the emission of large clouds of dust that would otherwise begenerated during the shredding process. Other shredders and crushers,including wet and dry shredders and crushers, may also be used so longas the required average particle size is attained. Super heavy dutyshredders of the general type described above are particularly preferredbecause of their ruggedness and capacity to receive unshreddableswithout damage and to reduce the debris to an appropriate particle size.

To more efficiently reduce the construction and demolition debris to theappropriate particle size, ferrous metal items may be optionally addedas a separate input stream to the shredder. Such additional ferrousmetal items function in the shredder in a manner similar to the balls ina ball mill to enhance the shredding process.

After shredding, the shredded material preferably undergoes a magneticseparation process as shown in blocks 20 and 22 to remove ferrous metalwhich can be of commercial value. The magnetic separator is preferably adrum type electromagnetic separator of conventional design. Afterferrous metals are removed, the shredded debris optionally undergoes anair or water separation process as shown in blocks 24 and 26 to recovervaluable non-ferrous metals such as copper, aluminum, etc.

If a wet shredder is used, the shredded, non-metallic debris is thendewatered, if necessary, as shown in block 28 to remove excess water sothat the resulting product has an acceptable moisture content. If a dryshredder is used, water is added to moisten the material to a desiredmoisture content so as to give it sufficient weight and consistency foruse as daily cover or for use in other applications according to theinvention. The moisture content may be in the range of about 5% to about45% by weight, is preferably in the range of about 10% to 14% by weightand most preferably about 12% by weight. Excess water from thedewatering step is preferably reused in the shredding step 18 if a wetshredder is employed or piped to the water separation step 24 if a dryshredder is used. If a dry shredder is used in the shredding step 18 andthe water separation step 24 is omitted, water 30 may be added to theshredded debris to raise its moisture content to a level above thedesired range before passing it to the dewatering step 28 to adjust themoisture content to the desired range. Dewatering is preferablyaccomplished in a dewatering press, but may be accomplished by othermeans or by natural drainage. A water source 32 is provided forsupplying additional water to the excess water 30 or for directlysupplying the wet shredder 18 and/or the water separator 24. Water flowis represented by dashed lines in the drawing.

The output of the dewatering step 28 is a product 34 in the form ofmoist recycled construction and demolition debris. The article producedaccording to the method of the present invention is suitable as analternative daily cover for all types of landfills including, municipalsolid waste, land clearing debris, rubble, and industrial wastelandfills, and for other uses as described hereinafter.

In the use of the product 34 in a landfill as daily cover, it may bedesirable to mix a quantity of ash with the product to aid inneutralizing acids in the landfill, especially in the leachate reachingthe bottom of the landfill site. Such addition of ash is particularlyadvantageous in cases where the quantity of cement, concrete and plasterboard in the construction and demolition debris is at a low level. Theash may be added to the product either before or after shredding.

FIG. 2 illustrates a fragmentary cross-section of a municipal solidwaste landfill 40 in which the product 34 made according to the processdescribed above is used as a daily cover. The landfill 40 comprises abase 42 which may be a landfill liner, a previously deposited landfillcell, an intermediate cover or the like. Landfill 40 comprises aplurality of alternating layers of shredded municipal solid waste 44 andthe shredded product 34 used, in this instance, as daily cover for theshredded municipal solid waste. Solid waste 44 may be shredded by anyknown wet or dry shredding process, as well as by the process describedherein.

The landfill 40 of the present invention advantageously provides acompact, highly compressible landfill that serves to dispose, of bothmunicipal solid waste and construction and demolition debris in the samelandfill with minimum use of earthen material in the landfill design.

FIG. 3 illustrates an embodiment of a temporary roadbed 50 in which theproduct 34 made according to the process described above is used tostabilize a temporary roadbed, especially such roadbeds in wet or marshyareas. Examples of locations where such temporary roadbeds areadvantageously used include landfill sites, logging areas, constructionsites, off-the-road recreation areas and the like. The temporary roadbed50 is formed over the existing ground or soil base 52 which may becovered or partly covered by surface or standing water or may bemoisture-laden, muddy or rutted from vehicular traffic. The shreddedproduct 34 is spread over the base 52 in layered amounts sufficient forthe initial layer or layers of product 34 to mix with the soil and soakup the moisture in a layer or region 54. An additional layer or layersof product 34 are spread over the region 54 to form a compressible roadsurface 56 over which vehicular traffic may pass without difficulty.

If water or moisture conditions recur, additional layers of the product34 may be spread over the surface of roadbed 50. A layer 58 of gravel oraggregate may also be spread over the top layer of product 34 althoughsuch layer 58 is not necessary.

A further related application of the product 34 is in soilstabilization. The product may be spread upon large or small land areaswhere soil stabilization or erosion control is desired. Since theproduct 34 has the capacity to absorb substantial amounts of water, itmay be applied to slopes or grades where water run-off is a problem.According to the invention, the product 34 is spread over the area to betreated and is preferably mixed with the underlying soil surface byequipment such as a bulldozer, front end loader or the like.

Because of its sponge-like qualities, the product 34 may also be used tosoak up spills of oil and other petroleum products on land areas byspreading the product, mixing it with the spill and the underlyingcontaminated soil and hauling the resultant mixture to an appropriatewaste disposal site.

The product 34 may also be advantageously combined in varying amountswith fly ash and used as a soil nutrient or with sludge and used as asoil nutrient or topsoil. While the particular ratio of the quantity ofproduct 34 to the quantity of fly ash or sludge is not critical,mixtures of 10%-50% or more by weight of fly ash or sludge arebeneficial.

Although certain presently preferred embodiments of the invention havebeen described herein, it will be apparent to those skilled in the artto which the invention pertains that variations and modifications of thedescribed embodiment may be made without departing from the spirit andscope of the invention. Accordingly, it is intended that the inventionbe limited only to the extent required by the appended claims and theapplicable rules of law.

What we claim is:
 1. A method of disposing of municipal solid waste andconstruction and demolition debris in a landfill comprising the stepsof:dumping a first layer of shredded municipal solid waste on a landfillsite; and applying a second daily cover layer over said first layer,said second layer comprising construction and demolition debris to whichwater is added during processing of the debris through a shredder into amoist shredded product.
 2. The method of claim 1, including the step ofapplying alternating layers of shredded municipal solid waste andshredded construction and demolition debris.
 3. The method of claim 1,including the step of adding ash to the shredded construction anddemolition debris of the second layer.
 4. A method of making a roadbedusing construction and demolition debris comprising the steps ofprocessing construction and demolition debris through a shredder, addingmoisture to the debris during processing of the debris through theshredder, spreading a layer of the shredded construction and demolitiondebris over an earthen surface and mixing a portion of the shreddedconstruction and demolition debris with a portion of the earthen surfaceto form a roadbed.
 5. The method of claim 4, including the step ofspreading a layer of gravel or aggregate over said layer of shreddedconstruction and demolition debris.
 6. A method of soil stabilizationcomprising the steps of processing construction and demolition debristhrough a shredder, adding moisture to the debris during processing ofthe debris through the shredder, spreading a layer of the shreddedconstruction and demolition debris over a soil surface to be stabilizedand mixing said shredded construction and demolition debris with atleast a portion of the soil of said surface.
 7. A method of making asoil nutrient comprising the steps of processing construction anddemolition debris through a shredder, adding moisture to the debrisduring processing of the debris through the shredder, mixing theshredded construction and demolition debris with a quantity of fly ashor sludge and applying the mixture to an area of soil.
 8. The method ofclaim 7, wherein the amount of fly ash or sludge in the mixture is 10%to 50% by weight.
 9. The method of claim 1, including the step ofcompacting the debris prior to processing the debris through theshredder.
 10. The method of claim 4, including the step of compactingthe debris prior to processing the debris through the shredder.
 11. Themethod of claim 6, including the step of compacting the debris prior toprocessing the debris through the shredder.
 12. The method of claim 7,including the step of compacting the debris prior to processing thedebris through the shredder.
 13. The method of claim 1, wherein water isadded to the debris to a moisture content of between about 5% to about45% by weight.
 14. The method of claim 4, wherein water is added to thedebris to a moisture content of between about 5% to about 45% by weight.15. The method of claim 6, wherein water is added to the debris to amoisture content of between about 5% to about 45% by weight.
 16. Themethod of claim 7, wherein water is added to the debris to a moisturecontent of between about 5% to about 45% by weight.